UFOs (unidentified floating objects)

The townsfolk are mystified "it looks like the same as last time , but  ...  "

It doesn't have the iridescence that is usually associated with oil on water.  A previous occurrence was thought originate in an industrial estate some miles away.  

There are no obvious signs of fish distress and the ducks are doing what ducks usually do in water.  So it's a mystery.  The water authority are on the case.